Process of rolling alloy steel



Patented Sept. 1, 1931 UNITED STATES PATENT OFFICE No Drawing.

Certain rollable and forgeable alloy steels, particularly those eonta'ining chrominum, aluminum and silicon, with or without nickel and (or) tungsten or molybdenum, are particularly adapted for use in the manufacture of special articles, especially valves. In the manufacture of valves from such alloy steel, the metal is first rolled into bars, from which the finished articles are forged. a

Great difiiculty at times may be experienced in rolling the nietal. Frequently the rolled product is cracked or otherwise defective, necessitating scrapping and remelting. Sometimes the rolled product is apparently sound but defects develop in the forging or in the finished article. obvious that if the problem of uniformly successful rolling could be overcome, it would be a decided contribution to the art.

As a result of experimental work done by 'John L. Cox, Francis B. Foley and myself jointly, it was discovered that if the alloy steel be of a strongly martensitic type, certain rolling procedures, associated with certain cooling and reheating procedures, re-

sulted in the production of steel bars that are free from surface defects, and are soft and readily shearable cold instead of being comparatively hard, as distinguished from steel bars resulting from the usual methods of rolling, which are frequently too hard and brittle to be cold sawn or sheared cold without cracking and fracturing, in such cases necessitating warming the bars in hot water or even in a furnace before shearing can safely be done. While such improved rolling procedures are also applicable if the alloy steel be of the austenitic type, I have discovered that it is possible to roll alloy steel of the latter type by a process which requires substantially less time, avoids reheating, and is substantially more economical. I also discovered that if the steel be martensitic in structure, the same procedure cannot be followed. The wholly different procedure which can be followed, with assurance of success, if the steel be martensitic in structure, forms the subject-matter of a Application filed November 20, 1929. Serial No. 408,672.

formation is required to enable those skilled 5s range wherein the steel is sufliciently plastic It is" "to this temperature, the rolling usuallywill separate application filed by the joint inventors. p

Methods of determining the structural character of steels are well known and no inin the art to determine this factor. It may be said, however, that martensitic steel tends to harden on cooling from a high heat in the air, while austenitic steel does not.

This affords one convenient method of deterr'nining structure.

If the alloy steel be austenitic in structure,

I have discovered that, on cooling, the alloy steel process through three definite temperature ranges, namely: A high, temperature to permit. of initial rolling; an intermediate temperature range wherein the steel becomes so relatively brittle that if the steel is rolled at that temperature cracks and tears are produced on the surface of the steel;-and a low temperature range wherein the steel again becomes sufliciently plastic to permit of final rolling. If the steel is rolled while within this high plastic temperature zone and is then allowed to cool through the intermediate temperature zone, the rolling may be completed within the low plastic temperaure zone. The resultant rolled product is free from defects. It is impossible to specify these three temperature zones with exactitude, since the ranges of temperature in each zone vary somewhat with different compositions The following example, however, may be given. Given a composition comprising carbon 0.50%, nickel 2.5%, chromium 11.32%, aluminum 2.08%, silicon 1.30% and manganese within the usual range in alloy steel making practice, and the remainderprincipally iron, and assuming the structure to have been determined to be austenitic after cooling freely from the initial temperature of rolling, the alloy steel is first brought to a temperature of about 217 5F or somewhat less and is rolled until it cools to a temperature not under about 2050F. When the alloy steel has dropped not have been completed. The steel is' then allowed to cool to about 17 50F, whereupon f rolling is resumed. The rolling is continued until completion. The lower limit of the second rolling temperature zone is when the steel becomes too rigid to flow satisfactorily. It is usually desirable, however, to complete the rolling before the alloy steel has cooled much below 1400 or 1500 F.

The approximate range of the first rolling temperature zone, which I call the high plastic temperature zone, and the approximate range of the intermediate zone, can be determined, in the case of each particular composition, by Well known suitable tests. When these zones are ascertained, they may be safely assumed to apply to austenitic alloy steel of the same composition. As a factor of safety, the initial rolling may be carried out well within the limits of the ascertained high plastic zone, and the final rolling may be started at a temperature reasonably close to, but safely below, the upper limit of the low plastic temperature zone.

Having now fully described my invention, what I claim and desire to protect by Letters Patentis:

l. The process of rolling steels containing substantial proportions of alloying metals including chromium, aluminum and silicon and which are found to be austenitic on cooling freely from the initial heat of rolling, which comprises rolling the steel While it is cooling within the range of its high plastic temperature zone, then allowing the steel to cool through an intermediate relatively nonplastic zone, without rolling the steel, to within the upper limit of its low plastic temperature zone, and resuming the rolling while it is cooling within the last named zone.

2. The process of rolling steels containing substantial proportions of alloying metals including chromium, aluminum and silicon and WhlCll are found to be austenitic on cooling freely from the initial heat of rolling, which comprises rolling the steel while it is cooling to a temperature not substantially under approximately 2050F., then allowing the steel to cool to approximately 17 50F. without rolling the steel and then completing the rolling while the alloy steel is cooling from the last named temperature.

In testimony of which invention, I have hereunto set my hand, at Philadelphia,

Pennsylvania, on this 11th day of Nov., 1929.

HOWARD M. GIVENS. 

